Resolution of dl-glutamic acid



` RESOLUTION OF DL-GLUTAMIC ACID Filed May 2'7, 1958 3 Sheets-Sheet lMM5 Fl E. 1

June 6, 1961 Filed May 27, 1958 J. L. PURVIS RESOLUTION OF' DL-GLUTAMICACID 3 Sheets-Sheet 2 June 6, 1961 Filed May 27, 1958 falla 3Sheets-Sheet 3 FII-5.3

' pure D-glutamic acid hydrochloride.

United States Patent O This invention relates to a process for resolvinga mix- Patented June 6, 1961 and terminating the crystallization after alimited period of time, preferably not substantially later than the timeat which maximum resolution occurs, and in any event before lspontaneousnucleation and crystallization of the non-seeded enantiomorph occur toany substantial extent.

- Generally, the point for terminating the crystallization will-bereached-in about 1 to about 60 minutes after. initiation thereof, mostcommonly in about l to about 60 ture of the optically `active isomers ofan alpha-amino aliphatic dicarboxylic acid, and more particularly, to a'process for resolving a racemic mixture of glutamic acid enantiomorphs.

It is well known that glutamic acid exists in D- and L- v'opticallyactive forms, as well as the racemic, or DL,

form. AOf these forms, only L-glutamic acid is of ecojnomic importanceat the present time, there being little known utility for D- orDL-glutamic acid. Chemical processes for the synthesis of glutamic acidhave invariably resulted in the formation of the racernic mixture; andin order for such processes to be commercially attractive, a simple,inexpensive method must be available for resolving the DL-glutamic acidand obtaining optically active L-glutamic acid. No such resolutionmethod has heretofore been described in the art.

Various resolution techniques have been attempted in' the past. -Menozziand Appiani (Atti R. Accad, Lincei (Roma), Rend. (5) 2, ll, 415 (1893))crystallized a mixture of D- and L-glutamic acids and manually sortedthe enantiomorphs according to their crystal form. This is the classicPasteur technique (Ann. Chim. Phys. (3) 24, 442 (1848)), of laboratoryinterest only. In connection with research on Imalignant tumors, Kogl etal. (Rec. trav. chim., 68, 387-96 (1949); C.A., 44, v1028 e) prepared aSolution containing 8 parts of radioactive DL-glutamic acidhydrochloride and 4 parts of non-radioactive D- glutamic acidhydrochloride, then seeded with a few crystals of the latter, andallowed the solute to crystallize. The product, amounting to 4.1 parts,was found to be Thus, all of the added D-glutamic acid hydrochloride wasrecovered, but no resolution of the racemate was eected. For resolving anumber of other racemic substances, Freudenberg successfully employedselective seeding of a supersaturated solution of the racemate withcrystals of one enantiomorph to produce selective crystallization of theseeded enantiomorph (Stereochemie, Franz Deuticke, 1933, p. 566). thepresent inventor in an attempt to resolve DL-glutamic When theFreudenberg method was tested by acid, however, it Was found that thecrystalline product was heavily contaminated with the non-seededenantiomorph, and that no commercially satisfactory separation wasobtained. Accordingly, none of the vmethods described in the art havebeen found feasible for the resolution of DL-glutamic acid on acormnercial scale.

A primary object of the instant invention is an effective process forseparating an enantiomorph of glutamic acid from a racemic mixture ofglutamic acid enantiomorphs, in which contamination of the product withthe minutes, depending upon such factors as solution temperature,soluteconcentration and degree of supersaturation,

- proportion of seed crystals, surface area of seed crystals, land thelike. YYIn general, the time required to reach maximum resolution variesdirectly as a function of the solution of seed crystals.

lizationafter a limited time, contamination of the prodtion temperatureand inversely as a function of the propor- By thus terminating thecrystaluctV with the non-seeded enantiomorph is substantially completelyavoided, and a high yield of the seeded enantiomorph in substantiallypure form is obtained.

'Ihe critical behavior of DL-glutamic acid in the process of the presentinvention is completely unexpected in view of Freudenberg. In studyingthe resolution of sodium ammonium DL-tartrate by selective seeding,Freudenberg reported that, after selective crystallization of the seededenantiomorph had been initiated, the solubility of the enantiomerincreased, and consequently there was no further reason for the latterto crystallize. In accordanceA with the present invention, it has beenfound that DL-glutamic acid behaves entirely diierently. After asupersaturated solution of DL-glutamic acid has been selectively seeded,the seeded enantiomorph crystallizes, but

`the crystallization of the non-seeded enantiomorph is noty therebyinhibited.- To the contrary, the non-seeded enantiomorph alsocrystallizes, apparently through spontaneous nucleation, initiated insome unsascertained way.

In investigating this phenomenon,- it was discovered that the undesiredspontaneous crystallization does not begin immediately after seeding,butonly after an induction period which normally ranges from about l toabout minutes. Within this period the degree of resolution of the seededenantiomorph rises to a maximum, then rapid- -ly drops olf-asthenon-seeded enantiomorph begins to crystallize. It is thereforecritically necessary in achieving a high degree of resolution that thecrystallization be terminated within such limited period, before anysubstantial amount of the Ynon-seeded enantiomorph hasspontaneouslycrystallized. It is especially preferred to terminate thecrystallization as soon as the degree of resolution levels oif, thispoint being readily determined by measuring the optical activity of theresidual solution. The optical rotation of the residual solution changesin the opposite direction to that of the solids, and clearly indicateswhen crystallization of the seeded enantiomorph has undesirably slowedand spontaneous` crystallization of the unseeded enantiomorph isimminent.

The present invention is effective `for resolving free DL- glutamicacid, DL-glutamic acid hydrochloride, or DL- In accordance with thepresent invention, Aa racemic V kglutamic acid mixture can besuccessfully resolved by seeding a supersaturated aqueous solutionthereofwith crystals of one glutamic acid'enar'rtioinorph,` therebyinitiating selective crystallization of the *said* enantiomorph,

,m following equation:

' glutamic acid hydrobromide, employing in each case seed crystals ofthe particular `compound in substantiallyv pure D-or L-form-as desired,and preferably operating at the natural pH of the particular compoundunder the solution conditions. v

AThe degree of--resolutionf as this term is used herein, refers to theproportion of the enantiomorph preferentially crystallized in opticallyactive form fromthe racemic solution, based upon the quantity of suchVenantiomorph originally present in the-racemate. The Vdegree ofresolution, R, is calculated as a percentage according to the 3 where Wis the total weight of the solids obtained in the preferentialcrystallization, A is the weight of contaminating enantiomorph therein,S is the weight of seed crystals employed, and B is the weight of theseeded enantiomorph in the original racemate, all weights being on drybasis.

In resolving free DL-glutamic acid, a supersaturated solution of thefree acid is prepared in any convenient manner. For example, DL-glutamicacid monohydrate can be slurried in water in the presence of asutiicient quantityof inorganic acid such as hydrochloric acid orsulfuric acid to produce complete solution, andthe pH of the resultingsolution can then be adjusted to around 3.2 (the isoelectric point offree glutamic acid) by adding alkali such as sodium hydroxide, calciumhydroxide, ammonium hydroxide, or the like. Alternatively, DL- glutamicacid monohydrate can be slurried in water in the presence of asuliicient quantity of alkali to produce complete solution, and the pHof the resulting solution can be adjusted to around 3.2 by addinginorganic acid.

The concentration of DL-glutamic acid in the resulting supersaturatedsolution will generally range between about 1.5 and about 8% by weightat temperatures between about 15 and about 40 C., varying as a directfunction therewith, and will preferably range between about 2 and about6% by weight, depending upon the desired degree of supersaturation. Atroom temperature (20 to 30 C.) the concentration will usually lie in therange of about 3 to about 4% by weight. The concentration of thesolution should preferably be such that the desired enantiomorph ispresent in a concentration from about l to about 100% in excess of thesaturation level under the existing temperature conditions, optimallybetween about 25 and about 50% To the solution thus formed is added aquantity of optically active glutamic acid seed crystals, that is,either L- glutamic acid or D-glutamic acid, the quantity of seedcrystals being preferably in the proportion of at least about 5% byweight of the seeded enantiomorph in the solution, optimally betweenabout 25 and about 50% by weight. The solution is then agitated gentlyto assist crystallization. The crystallization is suitably carried outat moderate temperatures, between about l5 and about 40 C., the rate ofcrystal formation being greater at the lower temperatures. The operationis most conveniently carried out at ordinary temperatures in the rangeof about 20 to about 30 C., in which range a high degree of resolutionis Aachieved without complications. The degree of resolution ordinarilyreaches a maximum in from about to about 60 minutes, depending primarilyupon the concentrationof the solution, the temperature, the degree ofsupersaturation, and the proportion and surface area of the seedcrystals, at which point the crystallization is terminated byfiltration, centrifugation, or the like. The crystallized solidscomprise, in addition to the seed crystals, a substantial proportion ofthe optically active form of glutamic acid present in the startingmixture which corresponds in rotation to that of the seed crystals. Y

In resolving DL-glutamic acid hydrochloride, a solution supersaturatedtherewith and having a pH below about 0.6 is conveniently prepared bycommingling DL-glutamic acid hydrochloride with water at a temperaturesniciently high to eiect complete dissolution, then cooling to thedesired resolution temperature, between about and about 40 C., optimallyaround 20 to 30 C. This is the preferred type of solution for thepresent invention, containing from about 40 to about 557%V by weight ofDL-glutamic acid hydrochloride, varying asv a` direct function of thetemperature and containing substantially no free hydrogen chloride.Alternatively, a solution can be prepared if desired by dissolving fromabout 5 to about 55% by weight of DL-glutamic, acid hydrochloride inwater and adding a suicient quantity of hydrogen chloride orconcentrated hydrochloric acid to render the solution supersaturated. Asa further alternative, DL-

glutamic acid monohydrate can be dissolved in dilute hydrochloric acidto yield the hydrochloride salt solution, and hydrogen chloride orconcentrated hydrochloric acid is thereafter added., The proportion offree hydrogen chloride in such a solution may range up to'around 30% byweight. The degree of supersaturation of the desired enantiomorph shouldbe in the rangeY of about l0 to about based on the saturation level,preferably between about 30 and about 60%. The supersaturated solutionis seeded with crystals of L-glutamic acid hydrochloride or D-glutamicacid hydrochloride, and crystallization of the seeded enantiomorph iscarried out as described above with referenceY to the resolution of freeDL-glutamic acid. The proportion of `seed crystals is suitably at leastabout 1% by weight, preferably around 5 to 10%, based on the weight ofthe seeded enantiomorph in the solution, when the solution contains nofree hydrogen halide, and at least about 5% by weight, preferablybetween about 25 and about 50%, when the solution contains free hydrogenhalide to produce supersaturation.

The resolution of DL-glutamic acid hydrobromide is carried out in amanner similar to that employed for the hydrochloride.

It has been found that the highest yield of resolved product per unitWeight of starting solution is obtained in a DL-glutamic acidhydrochloride system containing no excess hydrogen chloride. Thefollowing represents a highly advantageous procedure and set ofoperating conditions for the preferential crystallization of the L-isomer from the racemic solution: A solution containing 52% by weight ofDL-glutamic acid hydrochloride is seeded with pure L-glutamic acidhydrochloride crystals and stirred gently at 30 C. The seed crystals(-200 lmesh, U.S. Standard Sieve Series) are added in an amountequivalent to 5% by weight of the L-glutamic acid hydrochloride in thesolution., At the end of 30 minutes, the crystallization is terminatedby filtration, and the seed crystals are recovered, together with about32% of the L-glutamic acid hydrochloride originally in the solution. Thecrystals contain about 99% by weight L- isomer and about 1% D-isomer.They can readily be purified by dissolving in water, adjusting to pH 3.2With alkali, and crystallizing free L-glutamic acid. In this way, apurity closely approaching 100% is readily attainable.

The preferential crystallization method of the present invention iscapable, at best, of resolving only the portion of the seededenantiomorph which is supersaturated in the starting solution, leavingin every case a considerable quantity of the racemic mixture in theresidual solution,

together with the non-seeded enantiomorph. For economic reasons,therefore, it is important to employ some means for recovering theseglutamic acid values. For this purpose, the )following technique hasbeen developed (which for convenience will be described lwithV referenceto a process in which L-glutamic acid was the enantiomorph initiallyseeded and crystallized). From the resulting L-glutamic 4acid motherliquor is crystallized the supersaturated D-glutamic acid,vsubstantially equivalent to the L-isomer previously removed. Theremaining solution of racemic glutamic acid is recycled to the beginningof the process. The D-isomcr is converted to the racemic form by meanswell known to the art, and the racemate is recycled to the beginning ofthe process for additional L-glutamic acid recovery. y Y Y Theproportion of seed crystals may vary over a wide range. Some degree ofresolution can be obtained with a Very small quantity of seed crystals,c g., as little as 0.5% by weight, based on the DL-glutamic acidsubstance in solution, especially when the crystals are of small size.For any given solution and resolution temperature, however, there is anoptimum proportion of seed crystals which will produce the maximumdegree of resolution. For example, in resolving a solution containing4.98%

DL-gltamic acid hydrochloride and 25% of free hydrogen chloride at 25C., the minimum amount of seed A:Learn-54a crystals required to achievemaximum crystallization o f L-glutamic acid hydrochloride is equivalentto approximately 100% of the L-glutamic acid hydrochloride in thesolution. Greater proportions of seed crystals increase the rate ofAcrystallization substantially, but increase the degree of resolutionvery little. Smaller proportions result in both a slower crystallizationrate and a lower degree of resolution. Inasmuch as the non-seededenantiomorph tends to crystallize after -a limited time and tocontaminate the seeded enantiomorph, the seed crystals must be employedin a suicient proportion, as defined hereinabove, to produce the desiredcrystallization within less than such time.

The rate of resolution in the process of the invention is considerablyinluenced by the size of the seed crystals. In general, the electivenessof the seed crystals per unit weight increases greatly as` the crystalsize decreases. Thus, it is reasonable to conclude that the effects ofboth the size and the quantity of the seed crystals are directly relatedto the totalsurface area. thereof in any given case. IthasVbeen-observed, for example, that a given amount of finely ground seedcrystals of -200 mesh particle size range produced a faster rate ofresolution and also a slightly higher degree of resolution than the sameweight of the original unground crystals, which consisted of a mixtureof sizes with approximately 70% in the -|-60 mesh range.

DL-glutamic acid may be prepared by -any suitable process, such as, forexample, by the method disclosed in U.S. Patent 2,606,921 to Weisblatand Lyttle (August 12, 1952).

The supersaturated solutions of DL-glutarnic acid, DL-glutamic acidhydrochloride, or DL-glutamic acid hydrobromide utilized in carrying outthis invention may be prepared in anyA convenient manner. MonosodiurnDL- glutamate dihydrate, monoarnmonium DL-glutamate, monopotassiumDL-glutamate, DL-glutamic acid monohydrate, DL-glutamic acidhydrochloride, DL-glutamic acid hydrobromide, and other soluble metallicsalts and acidic salts can be utilized satisfactorily in preparing thesesolutions.

The attached ow sheets represent integrated processes embodying theinvention Vfor the complete resolution of DL-glutamic acid hydrochlorideto produce L-glutamic acid hydrochloride. The same procedures can beemployed with appropriate modicationsV to produceD-gluf tamic acidhydrochloride, if desired; and with other appropriate modifications theprocedures can be employed for the resolution of DL-glutamic acid and ofDL-glutamic acid hydrobromide. Such modiications will be obvious tothose skilled in the art from` the presentV description.

FIGURES 1 and 2 represent a process in which L-glutamic vacidhydrochloride is first selectively seeded, crystallized, and separated,and the mother liquor is treated to recover the remaining glutamic acidvalues for recycle.

FIGURE 3, in conjunction with FIGURE 2, represents a process in whichD-glutamic acid hydrochloride is first selectively seeded, crystallized,and removed, and L-glu tamic acid hydrochloride is recovered as thedesired primary product in essentially pure form by crystallization.from the mother liquor.

Referring now to FIGURE 1, 7.27 lb. of sol-id DL-glutamic acidhydrochloride (referred to-hereinafter for convenience as DLGA.HC1) aredissolved at about 60 C. in. 31".15 lb. of Filtrate A from a subsequentstep in the process, containing dissolved DL-GAHCl; The resultingsolution, weighing 3824 lb., contains 20;4 lb. ofv DL- GA.HCl Thesolution is decolorized, if desired, by add- 0.8 lb. of' activatedcarbon, stirring, ltering, and' washing` Withl 1.0 lb. o f-l water. Thecarbon cake is discarded or used topurify crude synthetic glutamic acid.rIhr lil'- tlatefand washingsV arc-combined and` cooled'. At 35 C., the.solution., is seeded with 0.456 lb. of L-GAHCl seed crystals of 200I53325 mesh size. Cooling is continued with gentle stirring to 30 C. A tthe end of 30 minutes after seeding, the mixture is filtered rapidly andthe filter cake is washed if desired with a small proportion of water,yielding 4.65 lb. of Wet solids containing 3.891 lb. of L-GA.HCland0.264 lb. of DGA.HCl. The cake -is dissolved in 27.43 lb. of water,and the pH of the solution isV adjusted to 3.2 with 1.81 lb. of aqueous50% sodium hydroxide solution. The solution is allowed to stand withstirring about 24 hours at 30 C. while crystallization of puriedL-glutamic acid proceeds, and the resulting slurry is filtered. Thesolids are washed with 5.0 lb. of water, yielding a wet cake equivalentto 3.627 lb. of dry L- GA.HC1, substantially free fromthe D-isomer. Ofthese solids, a portion equivalent to 0.562 lb. of L-GA.HC1 is withdrawnfor use in seed preparation. The remainder, 3.06 lb., calculated asL-GAHCl, represents the yield of puried L-isomer from the process. Thecombined filtrate and washings (termed Filtrate B in the drawing) arefurther processed as shown in FIGURE 2.

The filtrate, weighing 3.5.1 lb., =from the first L-GA.HClcrystallization is stirred gently for 24 hours at 30 C., duringwhichtime the D-GA.HC] spontaneously nucleates and crystallizes. Seedcrystals of D-GA.HC1 may be added if desired, to speed the process. Theresulting slurry is filtered. The filtrate (designated Filtrate A in thedrawing, and lweighing 31.15 lb.) is recycled to the beginningof theprocess, as described above. The solids, weighing 3.96;lb.r inwetcondition and containing 3.366 lb. of D-GA.HCl plus 0.196 lb. ofL-GAHCI, are -further processed as described in FIGURE 2.

Referring to FIGURE 2, the D-GA.HC1 solids from FIGUREY 1 are heated at190 C. for 24 hours to elect racemization, thereof. The resultingracemate is dissolved in water, adjusted to below pH 0.6 by adding anequivalent quantity of concentrated hydrochloric acid, and heated at theboiling point for 2 hours to hydrolyze the glutamic acid precursorstherein. The resulting solution of DLGA.HCl is decolorized withactivated carbon, then combined with a DL-GA cake from later in theprocess, and concentrated and cooled to permit crystallization ofDLGA.HC1. The DL-GA.HC1 is ltered off and washed,- andthe material thusrecovered (3.335 lb.) is recycled to the beginning of the process.

The L-GA mother liquor and washings (Filtrate B" in FIGURE 1),containing DL-glutamic acid equivalent to 0.528 lb,V DL-GAHCI, areoptionally combined with the DL-GA.HC1 mother liquor and washings, thenconcentrated to 5 lb., adjusted to pH 7.0 with 0.230 lb. of aqueous 50%NaOH solution, and further concentrated to the point of incipient NaClcrystallization. The NaCl is crystallized at 65 C., filtered ot (0.41b.), and discarded. The filtrate is adjusted to pH 3.2 with 0.284 lb.of 37% hydrochloric acid, and DL-GA is allowed to crystallize at; 20 C.for 24 hours. The DL-GA is, tilteled olf, Washed'with a small amountv ofwater, and recycled as notedl above for further treatment with theracemized D-GA.HC1 solids. The iltrate and washings, containing NaCl andglutamic acid values equivalent to only 0.106 lb. of DLGA.HC1, arediscarded.

FIGURE 3 illustrates an advantageous modification of the invention` inwhich D-GA.HC1 is Iirst selectively seeded, crystallized, and separated,and LGA.HC1 is thereafter crystallized. By removing the D-isomersupersaturation first, the D-isomer is prevented from contaminating theL-isomer during the subsequent crystallization thereof. With theexception of the reverse order of crystallization, the modified processgenerally follows the.- process of FIGURES 1 and 2. Solid DLGA.HC1 isdissolved in recycled DLGA.HC1 solution (Filtrate A). The solution iscooled, seeded with crystals of D GA.HC1, and allowed to crystallize fora limited period as in FIGURE 1, suitably until the D-GA.HC1supersaturation approaches or reaches exhaustion, the crystallizationbeingv stopped,` however, before any sub,- stantial proportion of theL-isomer crystallizes. The

D-,GAHCl solids are then separated and further processed as in FIGURE 2.From the mother liquor, 1 -GA.HC1 is crystallized, optionally afterseeding with LGAHCI crystals. The L-GA.HC1 is filtered off, and themother liquor (DLGA.HC1 Filtrate A) is recycled to the beginning of theprocess. The solids are substantially pure L-GA.HCl, which can befurther purified by ythe simple recrystallization involved in convertingfrom the hydrochloride salt to free L-GA. 'I'his is done by dissolvingthe L-GA.HCl in water, adjusting the solution to pH 3.2 with sodiumhydroxide solution, crystallizing, filtering, and washing. The productis substantially pure LGA. The mother liquor (Filtrate B) contains aquantity of DL-GA, and is recycled to FIGURE 2.

The following examples illustrate specific embodiments of thisinvention. All parts and percentages are by weight unless otherwiseindicated.

Example 7 The following data illustrate the way in which the degree ofresolution varies with the time of crystallization in the presentinvention. In the test reported, an aqueous solution containing 9.96% ofDL-glutamic acid hydrochloric and 18% excess hydrochloric acid wasprepared by slurrying the required, amount of DL-glutamic acidmonohydrate in water and adding a sucient quantity of concentrated (37%)hydrochloric acid to dissolve the material and to supersaturate thesolution. To the resulting solution, adjusted to 30 C., were added 25%ofunsized crystals of L-glutamic .acid hydrochloride, based upon theL-gultamic acid hydrochloride in the solution, about 70% of the saidcrystals being in the -1-60 mesh range. The crystallization period wasmeasured from the time that the addition of the L-glutamic acidhydrochloride crystals was completed. The solution was agitated gentlythroughout the crystallization period, and samples were withdrawn fromtime to time for analysis and for calculation of the degree ofresolution. The results were as follows:

Example 2 The following data further illustrate the way in which thedegree of resolution varies with the time of crystallization intheprocess of the present invention. In the reported test, 525 parts of asaturated solution DL-gluin the D{-60 mesh range. The crystallizationmixture was sampled from time to time as in the previous example todetermine the degree of resolution. The results were as follows:

Time, min.: Resolution, percent 10.1 18.1 26.0 40 26.0 ys0 l26.0 i 6026.0

Two ofthe factors which influence the amount and the pate of`crystallization of optically active glutamic acid tamic acid preparedfrom 21.2 parts DL-glutamic acid 5? monohydrate and having a pH of about3.2 was seeded at 30 C. by admiring therewith about 10 parts of pure,unscreened L-glutamic acid crystals having about 70% Example 3 s Asolution containing 52% by weight of DLGA.HCl and no excess HC1 isseeded with 10% by weight of 200 mesh L-GA.HC1 crystals, based on theL-GA.HC1 in solution, and L-GA.HC1 is crystallized at 30 C.Theresolution reaches a maximum in about 30 minutes, and the crystallineproduct corresponds to about 8 parts by weight of L-GA.HC1 pet 100 partsof solution, equivalent to 31% resolution.

A solution containing 4.44% by weight of DLGA.HCl and a 25% excess ofHCl is similarly seeded and crystallized. In this case also, theresolution reaches a maximum in about 30 minutes, but the productcorresponds to only about l.1 part by weight of L-GA.HC1 per 100 partsof solution. On the other hand, this represents resolution.

Example 4 To illustrate the effect of the degree of supersaturation onthe rate as well as the extent of crystallization, DLGA.HCl solutions attwo supersaturation levels were seeded with 5% by weight of -200 meshL-GAHCI crystals, based on the weight of L-GA.HC1 in solution, andcrystallization was carried out at 30 C. The results were as follows:

DL-GA. HC1 concn, wt.-percent 52 55 DL-GA. HG1 supersaturatlon, percentof o! saturation 20. 4 27. 3

Degree of Resolution, Percent Example 5 A further factor whichinfluences the resolution of DL- glutamic acid is the proportion of seedcrystals used to induce crystallization. In a series of tests at 25 C.on solutions containing 4.98% by weight of DLGA.HCl and 25% excess HC1,it was found that maximum resoluvtion of I -GA.HCl was obtained byseeding with 100% of LGA.HCl crystals based on the weight of LGA.HCl inthe racemic solution, the seed crystals having the following screenanalysis:

' Mesh Percent +40 44.4 40-60 25.4 -100 21 -100 9.3;

From the resulting data, tabulated below, it is seen that greaterproportions of seed crystals increase the rate of crystallizationsubstantially, but increase the extent of crystallization very little.Lower proportions of seed crystals result in both slower rates and lowerdegreesy of crystallization. 'i 'I Y Beedproportlon,percent..`.`.-.. `9YAY18 '36 904 300 Degree of Resolution, Percent Timeline 1 37.2 3 41.0 535.9 45.9 8- 48.4 ln 44.5 37.5 47.0 22.4 33.4 38.9 48.3 44.5 45.9 an211s 43.1 37.2 35 37.2 47.3 27.3 40 37.2 41.6 13.6

' 'Example' About 28 parts of DL-glutamic acid monohydratc were slurriedin about 122 parts of water and dissolved by addition of aboutl 25 partsof 37% hydrochloric acid. After the DL-glutamic acid monohydrate wascompletely dissolved, an additional 325 parts of 37% hydrochloricacidwere added, so that the iinal solution amounted to 500 parts andcontained about 26% hydrogen chloride. Immediately after the finaladdition of hydrochloric acid, about 10 parts of unsized `L-glutamicacid hydrochloride crystals were added and the slurry was agitatedslowly 'to permit crystallization of solids from solution. After about16 minutes-of crystallization time the crystals were removed from theslurry by iltration.V The resolution-of the DL-glutamic acid by thisprocedure amounted 5 9qaiAV ..4 ,i

Example 7 About 51.3 partsiof monosodium DL-glutamate dihydrate weredissolved in 700 parts of water at 25 C.

. yThe solution was adjusted to pH 3.2 by'addition of suii- 'cient 37hydrochloric acid. To this solution, which was supersaturated withvrespect Yto DL-glutamic acid,

Example 8 About 21.2 parts of DL-glutamic acid monohydrate weredissolved in waterinthepresence of about 6 parts of' sulfuric acid andthe solution was diluted with water to 500 parts. ThepH ofthe solutionwas then adjusted to about 3.2 by addition of a snflicient quantity of a33% aqueous slurry'of 'calcium'hydroxide The temperature ofthe adjustedsolution was C. Pure, unsized L- glutamic acid'cry'stls'inthe'amount ofabout l0 parts were then added'to the adjusted Vsolution immediatelyvand gentle agitation was begun to permit crystallization of solids.After about 30 minutes the crystals were re- Ymoved by filtration andanalyzed. i The resolution of the pound selected from the groupconsisting of DL-glutamic acid hydrobromide, which comprises Vaddingseed-"crystals of said glutamic acid compound in one 'of its opticallyactive forms to an aqueous solution V'containing said DL-glutamic acidcompound at a supersaturation of at least about 10%, based on thesaturation level, the proportion of seed crystals being atleast aboutv1%v by weight of the seeded enantiomorph in thev solution in the case ofthe said DL-glutamic acid hydrohalides wherein the correspondinghydrogen halide is present in yfree form, and at least about 5% byweight of the seeded enantiomorph in the solution in the case ofsolutions containing said DL-glutamic acid compound without freehydrogen halide; crystallizing.l solids Vfrom Vthe solution,

vsaid crystallized solids being initially said glutamic acid compound ofoptical activity corresponding-to theV seed DL-glutamic acid by thisprocedure amounted to 32%.

The invention described and claimed in the present application is fullydescribed in my earlier applications, Serial No. 475,297, filed December14, 1954, now abandoned, and Serial No. 599,358, tiled July 23, 1956,now abandoned, the latter having been copendent with both thelater-tiled present application and the earlier-tiled Serial No.475,297. 'Ihe present application is accordingly a continuation-impartof Serial No. 599,358, and, through the latter, of Serial No. 475,297.

In accordance with the foregoing description, the following claimsparticularly point out and distinctly clalm the subject matter of thepresent invention:-

1. A process for resolving a DL-glutamic acid comcrystals, andseparating the crystallized solidsfrom the resulting slurry beforespontaneous nucleation-andcrys tallization of any substantialproportion'of the .nonseeded enantiomorph takes place and at a pointintime not substantially later thany the attainment of themaximum degreeof resolution R, calculated as 'i Vsolids are separated from the'resulting slurry within about 1 to about 60 minutes followinginitiationofcrystallization. f

3. A process as in claim 2 wherein said crystallization is carried outat the natural pH of said glutamicacid compound under the solutionconditions.

4. A process as in claim 3 wherein glutamic acid hydrobromide ispreferentially crystallizedfinoptically active form at a pH below about0.6 from a supersaturated solution of racemic glutamic acidhydrobromide, Y 5. A process asin claim 4 wherein said solution containshydrogen bromide in free form.l-

6. A process as in claim 3 wherein optically active glutamic acid'ispreferentially crystallized-from asupersaturated'solution of DL-glutamicacid ata pH around 7. A process as in claim 3 wherein 4glutamic acidhydrochloride is preferentially Vcrystallized in-optically active format a pH below about 0.6 from a supersa'turated solution of racemicglutamic acid hydrochloride.

8. A process as in claim 7 wherein said solution contains hydrogenchloride in free form.

9. A process for resolving DL-glutamic acid which comprises addingcrystals of glutamicacid in one of its optically active vforms toasuper-saturated solution of DL- glutamic acid wherein the concentrationof'DL-glutamic acid is between about l0 and about 100% greater than thesaturation level, the proportion of said added crystals being at leastabout 5% by weight, basedon the weight ofthe seeded enantiomorph in.said solution, crystallizing the enantiomorph corresponding to-V saidcrystals from the solution at a temperature between about 15 and about40 C. and a pH of about 3.2, and separating the crystallizedenantiomorph from the resulting slurry within about 10 to about 60minutes following initiation of crystallization to terminatecrystallization within a period of time not substantially greater thanthat in which maximum resolution is reached and to prevent contaminationof the seeded enantiomorph by spontaneous crystallization of itsenantiomer.

lO. A process for resolving DL-glutamic acid which comprises preparingan aqueous solution thereof containing DL-glutamic acid at aconcentration between between about 25 and about 50% greater than thesaturation level, adding thereto between about 25 and about 50% ofL-glutamic acid crystals based on the weight of DL-glutamic acid in thesolution, crystallizing L-glutamic acid from the solution at atemperature between about 20 and about 30 C. and a pH around 3.2, andseparating the L-glutamic acid crystals from the resulting slurry withinabout to about 60 minutes following initiation of crystallization toterminate crystallization Within a period of time not substantiallygreater than that in which maximum resolution is reached and to preventcontamination of the L-glutamic acid by spontaneous crystallization ofD-glutamic acid. Y

1l. A process for resolving DL-glutamic acid hydrochloride whichcomprises adding crystals of glutamic acid hydrochloride in one of itsoptically active forms to a supersaturated solution of DL-glutamic acidhydrochloride wherein the concentration of DL-glutamic acidhydrochloride is between about 10 and about 100% greater than thesaturation level, the proportion of said added crystals being at leastabout 1% by weight, based on the weight of the seeded enantiomorph insaid solution, crystallizing the enantiomorph corresponding to saidcrystals from the solution at a temperature between about and about 40C. and a pH below about 0.6, and separating the crystallizedenantiomorph from the resulting slurry within about 10 to about 60minutes -following initiation of crystallization to terminatecrystallization within a period of time not substantially greater thanthat in which resolution reaches a maximum and to prevent contaminationof the seeded enantiomorph by spontaneouscrystallization of itsenantiomer.

l2. A process for resolving DL-glutamic acid hydrochloride whichcomprises preparing an aqueous solution thereof containing DL-glutamicacid hydrochloride at a concentration between about 30 and about 60%greater than the saturation level, adding thereto between about 25 andabout 50% of L-glutamic acid hydrochloride crystals based on the weightof L-glutamic acid hydrochloride in the solution, crystallizingL-glutamic acid hydrochloride from the solution at a temperature betweenabout and about 30 C. and at a pH below about 0.6, and separating theL-glutamic acid hydrochloride crystals from the resulting slurry withinabout 10 to about 60 minutes following initiation of crystallization toterminate crystallization within a period of time not substantiallygreater than the time in which maximum resolution is reached and toprevent contamination of the L-glutamic acid hydrochloride byspontaneous crystallization of D-glutamic acid hydrochloride.

13. A process for resolving a DL-glutamic acid cornpound selected fromthe group consisting of DL-glutamic acid, DL-glutamic acidhydrochloride, and DL-glutamic acid hydrobromide, which comprises addingseed crystals of said glutamic acid compound in one of its opticallyactive forms to an aqueous solution containing said present in freeform, and at least about 5% by weight of the seeded enantiomorph in thesolution in the case of solutions containing said DL-glutamic acidcompound without free hydrogen halide; crystallizing therefrom theenantiomorph corresponding in optical activity to the seed crystals tothe extent possible without spontaneous crystallization of anysubstantial proportion of the enantiomer, separating the resultingcrystals, and thereafter crystallizing glutamic acid compound of theopposite optical activity therefrom in substantially pure form.

14. A process for resolving DL-glutamic acid hydrochloride whichcomprises adding crystals of D-glutamic acid hydrochloride to an aqueoussolution containing DL-glutamic acid hydrochloride at a supersaturationbetween about 10 and about 100%, based on the saturation level, theproportion of seed crystals being at least about 5% by Weight of theseeded enantiomorph in the solution, crystallizing D-.glutamic acidhydrochloride from said solution over a period of about 10 to about 60minutes until the supersaturation thereof is exhausted to the extentpossible without spontaneous crystallization of any substantialproportion of L-glutamic acid hydrochloride, separating the crystallizedmaterial, and thereafter crystallizing L-glutamic acid hydrochloride insubstantially pure -form from the remaining solution.

15. A cyclic process for resolving a DL-glutamic acid compound selectedfrom the group consisting of DL- glutamic acid, DL-glutamic acidhydrochloride, and DL- glutamic acid hydrobromide which comprises addingcrystals of said glutamic acid compound in one of its optically activeforms to an aqueous solution containing said DL-glutamic acid compoundat a supersaturation between about 10 and about 100%, based on thesaturation level, the proportion of seed crystals being at least about5% by weight of the seeded enantiomorph in the solution, crystallizingtherefrom over a period of about l0 to about 60 minutes the enantiomorphcorrespending in optical activity to the added crystals withoutspontaneous crystallization of any substantial proportion of theenantiomer, separating the crystallized material from the resultingslurry, crystallizing glutamic acid compound of opposite opticalactivity from the remaining solution, separating the latter crystallizedmaterial from the resulting slurry, leaving a substantially racemicsolution, subjecting one of the crystalline materials to racemization,and recycling the racemic solution and racemate to further resolutionaccording to the dened procedure.

References Cited in the tile of this patent UNITED STATES PATENTS2,683,739 Weidman July 13, 1954 A 2,734,919 Amiard et al. Feb. 14, 1956FOREIGN PATENTS 2,972-56 Japan Apr. `20, 1956 OTHER REFERENCES Gilman:Organic Chem. (2nd ed.), vol. I (1938), pages 254-5.

Houben: Die Methoden der Org. Chem., vol. 2 (1943), page 1065.

1. A PROCESS FOR RESOLVING A DL-GLUTAMIC ACID COMPOUND SELECTED FROM THEGROUP CONSISTING OF DL-GLUTAMIC ACID, DL-GLUTAMIC ACID HYDROCHLORIDE,AND DL-GLUTAMIC ACID HYDROBROMIDE, WHICH COMPRISES ADDING SEED CRYSTALSOF SAID GLUTAMIC ACID COMPOUND IN ONE OF ITS OPTICALLY ACTIVE FORMS TOAN AQUEOUS SOLUTION CONTAINING SAID DL-GLUTAMIC ACID COMPOUND AT ASUPERSATURATION OF AT LEAST ABOUT 10%, BASED ON THE SATURATION LEVEL,THE PROPORTION OF SEED CRYSTALS BEING AT LEAST ABOUT 1% BY WEIGHT OF THESEEDED ENANTIOMORPH IN THE SOLUTION IN THE CASE OF THE SAID DL-GLUTAMICACID HYDROHALIDES WHEREIN THE CORRESPONDING HYDROGEN HALIDE IS PRESENTIN FREE FORM, AND AT LEAST ABOUT 5% BY WEIGHT OF THE SEEDED ENANTIOMORPHIN THE SOLUTION IN THE CASE OF SOLUTIONS CONTAINING SAID DL-GLUTAMICACID COMPOUND WITHOUT FREE HYDROGEN HALIDE, CRYSTALLIZING SOLIDS FROMTHE SOLUTION, SAID CRYSTALLIZED SOLIDS BEING INITIALLY SAID GLUTAMICACID COMPOUND OF OPTICAL ACTIVITY CORRESPONDING TO THE SEED CRYSTALS,AND SEPARATING THE CRYSTALLIZED SOLIDS FROM THE RESULTING SLURRY BEFORESPONTANEOUS NUCLEATION AND CRYSTALLIZATION OF ANY SUBSTANTIAL PROPORTIONOF THE NONSEEDED ENANTIOMORPH TAKES PLACE AND AT A POINT IN TIME NOTSUBSTANTIALLY LATER THAN THE ATTAINMENT OF THE MAXIMUM DEGREE OFRESOLUTION R, CALCULATED AS